For example, in Patent Document 1, a twisted vane centrifugal fan is described in that on each blade front-edge, the position of a side plate connection position is off-set relative to that of a main plate connection portion by a predetermined value in a rotational direction of an impeller.
Also, in Patent Document 2, a turbo fan and an apparatus having the turbo fan mounted thereon are described in that a blade of an impeller has a horizontal sectional curved shape, in which from the blade front-edge to the position where radius is R about a center axis, the more the blade proceeds toward the outer circumference of the impeller, the more the blade becomes positioned rearward in the rotating direction of the impeller, and from the position where radius is R to a blade rear-edge, the blade shape approaches a parallel line with an extended line connecting the center axis to the position where radius is R, so that the blade on the outer circumferential side from the position where radius is R is curved in the rotating direction to the blade on the inner circumferential side.
Furthermore, in Patent Document 3, a flush-mounting ceiling-type air conditioner having a conventional centrifugal fan mounted thereon is described in that at a position located apart from a ceiling air conditioner body, a ceiling plane suction port is provided while a side wall of the body is provided with a body suction port having a filter. A heat exchanger is provided on the back of the body suction port to oppose it. Within a space surrounded by an air guide plate and a ceiling panel, a blower is arranged. The ceiling panel mounted on the bottom of the body is provided with only a ceiling panel blow out port.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. H05-39930    [Patent Document 2] Japanese Unexamined Patent Application Publication No. H07-4389    [Patent Document 3] Japanese Unexamined Patent Application Publication No. H04-263710